It is customary in situations of critical electrical power requirements to provide an auxiliary power source which can be switched to and from the load in the event of commercial power failure or excessive power variations. In some situations, however, the criticality of the load is such the interruptions or variations in power caused by such switching, although slight, cannot be tolerated. For example, during the countdown period prior to the launch of a space vehicle, it is very important that the power supply and the load to the various computers and data equipment be uninterrupted. Typically, computer systems require a constant power supply. Interruptions in the power supply can erase memory and injure the software and hardware of the computer. Other situations where uninterrupted power supplies are considered important include: automatic banking services, automatic industrial processes, communication and signaling centers for maritime and aerial transportation, radio and television stations, and various emergency and security services.
Commercial power alone is generally not considered to be sufficiently reliable as a source of power for such usages. Interruptions commonly occur and loads may vary as other users come on and off the commercial power line. These problems are enhanced in the lesser developed countries where power systems are only in the initial stage of development.
Uninterruptible power systems are generally known within the prior art. Such uninterruptible power supplies usually comprise a generator and two prime movers, one of which normally drives the generator, and the other normally being stationary. When the normally operating prime mover ceases to function for any reason, the normally stationary prime mover is brought up to speed and is connected to drive the generator, usually through a clutch, thereby insuring a continuous supply of power from the generator. Commonly, a kinetic energy supply and device such as a flywheel or a DC dynamoelectric machine is coupled to the generator and supplies energy thereto during the transitional period when the generator load is being transferred from one prime mover to the other. One prior art type of no-break power supply comprises an internal combustion engine adapted to be connected through a normally disengaged clutch to a flywheel, the flywheel being connected in turn to the rotor of an electric generator which in turn is connected to the rotor of an AC motor. Another prior art type of no-break power supply employs a DC dynamoelectric machine in place of the flywheel, both of these devices acting to supply kinetic energy during the forementioned transitional period.
In the operation of a prior art no-break power supply of either of the aforementioned types, the generator and kinetic energy supplying device are normally driven by the A.C. motor. When there is a failure of the A.C. motor, as, for example, may be caused by an interruption in the power supplied to the A.C. motor, the internal combustion engine is started automatically, brought up to speed, and the clutch is then engaged. The internal combustion engine then drives the generator. During the transitional period when the load is being shifted from one prime mover to the other, the kinetic energy of the flywheel or DC machine is utilized to maintain the rotation of the generator.
U.S. Pat. No. 4,460,830 describes an uninterruptible power supply system that achieves many advantages not found in the prior art. In particular, this is a power system providing an uninterruptible power supply to an external load comprising a first generator adapted to supply energy to the external load, a first motor adapted to be connected to a source of power external to the power system, a standby generator electrically connected to the first motor, and a standby motor drivingly connected to the first motor. This uninterruptible power supply provides a constant source of power to the external load while isolating the external load from variation that may occur in the utility line.
This device and other common UPS systems, although effective in preventing interruptions in power supplies, has an initial capital cost that is difficult to recapture during the years of use of the device. In addition, a diesel engine of considerable size is required, although used during times of electrical blackout or shortage.
It is a object of the present invention to provide an uninterruptible power supply system that provides power to an external load without relying on the main utility source.
It is another object of the present invention to provide for cogeneration of electricity during the production of energy for the external load.
It is another object of the present invention to provide an uninterruptible power supply system that has a relatively quick payback of the initial cost.
There is still a further object of the present invention to provide an uninterruptible power supply system that has low maintainence requirements and costs.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.